Stamping is an operation whose purpose is to deform a flat raw part, known as a blank, between a die and an effector comprising a rigid punch or a bladder, in order to urge the blank against the die so that it fits its shape, and to conform said blank to a tridimensional shape. In the case of stamping a blank made of a composite material with a fibrous reinforcement, in the form of continuous fibers, this shape modification implies inter-laminar slipping between the plies and, locally, modifications of the distance between the fibers in controlled proportions, for passing from the plane configuration to the shaped configuration, the fibers not being able to deform plastically. These inter and intra-laminar movements of the reinforcements are made possible by the matrix viscosity, the matrix being brought to its melting temperature for performing the stamping of a blank with a thermoplastic matrix.
Thus, the typical steps for the stamping a thermoplastic matrix composite blank comprise:                heating the blank beyond its melting temperature: this operation leads to the deconsolidation of the blank which loses its rigidity. Thus, this operation is generally performed while the blank lies on a film capable of resisting to the temperature, such as a polyimide film.        transferring the blank, with its holding film, on the die, said die being generally pre-heated to a temperature lower than the melting temperature        stamping;        cooling of the workpiece between the punch and the die and its re-consolidation.        
This method of shaping is satisfactory, but presents some drawbacks related notably to the use of the polyimide film. Actually, being stamped with the blank, said film is not reusable, although being of a high price when the polymer constituting the composite matrix exhibits a high melting point, for example PEEK. In addition, as the film is not plastically deformable at the stamping temperature, it tends to wrinkle during this operation, the wrinkles being printed in the piece and causing fibers undulations.
Document FR 2 922 276 describes a method and a device for stamping a machined composite blank with a consolidated thermoplastic matrix; said device uses a transfer frame, that holds the blank on its periphery, without a support film, both during the heating and the transfer of the blank on the die. This same device of the prior art uses a locator traversing a bore made in the blank, which allows to position the blank in relation to the frame. This device of the prior art proves to be poorly reliable in the framework of an industrial production. In fact, the loss of the mechanical properties of the blank during heating frequently leads to its falling from the frame and even when the blank is further held by the locator, the bore tends to deform around said locator, leading to defects such as resin squeezing, pinching or undulations of the fibers; these defects, considering the continuous nature of the fibers, are likely to propagate at remote distances from the locator. During stamping, if the blank does not succeed in escaping from the locator, the latter causes tearing and hinders the interlaminar slipping, thus leading to defects.
The document FR 2 354 870 describes a device for stamping of a thin sheet of a thermoplastic material serving as coating to a container. Such a thin sheet, non-reinforced by fibers, tends to shrink during heating. For avoiding this phenomenon, the sheet is hooked on needles on its periphery. For avoiding the sheet tearing during stamping, a blank holder is used to wedge the edges of the sheet between the needles and the formed part. Such a method cannot be used in the case of a continuous fibers reinforced composite blank, the blank holder preventing the interlaminar slipping that is required for the forming. The term “machined blank” designates a blank which underwent a preparation, especially by material removal usually by high pressure water jet cutting or by routing with a cutting tool, in order to bring it to an adapted contour, or for cutting out particular shapes, such as a bore or a recess.